Tilted element and tilted screen antenna

ABSTRACT

To provide broadband directive radiation, a spade-shaped monopole radiator and a backscreen parallel to said radiator are mounted at an angle with respect to a ground plane. Said monopole is fed against ground by an RF source. In a preferred embodiment, according to the same principle, an array of spade-shaped monopoles are mounted parallel to a backscreen and at an angle with a ground plane to provide a steerable radiation pattern. In a preferred one of a number of modifications, spade-shaped monopoles are mounted symmetrically about the plane of symmetry of a Vee-shaped reflector. In said embodiment, said monopoles are also substantially parallel to said reflector.

United States Patent [72] Inventor Arthur F. Lyle Rocke Olney, Md. [21] App1.No. 874,743 [22] Filed Nov. 7, 1969 [45] Patented Oct. 5, 1971 [73] Assignee International Telephone and Telegraph Corporation Nutley, [54] TILTED ELEMENT AND TILTED SCREEN ANTENNA 5 Claims, 5 Drawing Figs.

[52] US. Cl 343/834, 343/835, 343/848 [51] Int. Cl H0lq1/48, l-l01q 21/00,1-l01q19/10 [50] Field of Search 343/825-831, 833-838, 845848, 907-916, 841,

[56] References Cited UNITED STATES PATENTS 1,892,253 12/1932 Schelleng 343/827 X 2,412,249 12/1946 Brown et al. 343/795 X 2,691,102 10/1954 Masters 343/817 X .2- TRANSMITTER 2,714,659 8/1955 Johnson et al... 343/795 2,935,746 5/1960 Marston et a1. 343/912 X 3,409,893 11/1968 Siukola 343/806 X OTHER REFERENCES The A.R.R.L. Antenna Book The American Radio Relay League, Inc. West Hartford, Conn. 1960 TK6565A6A6 pages 205- 206 ABSTRACT: To provide broadband directive radiation, a spade-shaped monopole radiator and a backscreen parallel to said radiator are mounted at an angle with respect to a ground plane. Said monopole is fed against ground by an RF source. In a preferred embodiment, according to the same principle, an array of spade-shaped monopoles are mounted parallel to a backscreen and at an angle with a ground plane to provide a steerable radiation pattern. In a preferred one of a number of modifications, spade-shaped monopoles are mounted symmetrically about the plane of symmetry of a Vee-shaped reflector. In said embodiment, said monopoles are also substantially parallel to said reflector. I

TILTED ELEMENT AND TILTED SCREEN ANTENNA BACKGROUND OF THE INVENTION I. Field of the Invention The subject invention relates to a screen-reflector-type antennas and more particularly to those of a type wherein the antenna elements are mounted at an angle with respect to a plane of symmetry defined by the antenna elements and their mirror images.

2. Description of the Prior Art The use of a screen-reflector in conjunction with a dipole or a monopole is well known. However, when the monopole combination is oriented vertically, wideband operation is not efficiently achieved. In order to overcome this difficulty, it has been a standard practice to tilt the monopole in the direction of desired radiation. This technique has yielded low elevation angles but has increased the amount of power radiated upwards. Said undesired radiation constitutes a waste of power which lowers antenna efficiency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide improve antennas of the screenreflector type.

According to the invention, there is provided a broadband antenna comprising antenna means having an axis of substantial symmetry, reflector means substantially parallel to said axis of symmetry; and means for providing a mirror image of said antenna means such that said axis of symmetry forms an angle with a plane of symmetry formed between said antenna means and its minor image.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other objects of this invention will become apparent by reference to the following description in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective illustration of a reflector-type antenna according to the invention;

FIG. 2 is a perspective illustration of a modified embodiment of the invention representing a reflector-type antenna having an array of radiators;

FIG. 3 is a perspective illustration of a dipole array reflector-type antenna according to the invention;

FIG. 4 is a perspective illustration of an antenna comprising a cone and a reflector according to the invention; and

FIG. 5 is a perspective illustration of an antenna comprising a folded triangular monopole and a reflector according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Many antennas are made unidirectional by employing a reflecting screen. In practice, in addition to the desired result, the antenna sees its image in the screen and, with the image, forms an unwanted secondary radiator which has a maximum radiation in the plane of the screen. This secondary radiator has side lobes that are usually considered to be back lobes of the wanted primary radiation.

To minimize these back lobes, according to one aspect of the invention, the axis of symmetry of the radiating element is maintained substantially parallel to the screen so that the element forms a transmission line with its image in said screen. The screen therefore continues its function of reflecting the primary radiation but ceases to act as an efficient secondary radiator.

In a first embodiment, as shown in FIG. I, a flat radiator 3 and a backscreen 2 parallel thereto are supported at an angle with respect to ground plane 1 by nonconducting members 10, 11 and 12. Said radiator 3 is fed RF energy from a transmitter 4 via RF transmission line 5.

In said embodiment, the spacing between the radiator and the backscreen is chosen, by using skills well known to those versed in the art, to provide desired radiation patterns and impedance characteristics. The height of the screen relative to the height of the radiator determines how strongly the radiator is illuminated in an undesirable way by waves diffracted over the top of the screen. Therefore, this height is preferably chosen; so that the response to such diffracted waves is of the same order of magnitude as the response due to the diminished secondary radiation. The width of the screen is preferably chosen so that the radiator lies in its shadow and, consequently, this is a function of the spacing of the radiator from the screen. In order to provide a radiator which is substantially parallel to the screen, the radiator should be of a symmetrical or flat nature. In said first embodiment, a rectangular form and a triangular form adjacent to one side of said rectangular form define a spade shape having a longitudinal axis of symmetry B and anapex A, which is used to provide a flat broadband radiator. Power is coupled to said radiator at the. apex by using coupling techniques well known in the art. In the invention as above described, the radiator and/or its associated screen may be constructed from either solid sheet or openwork conducting material. Ideally, the above-mentioned ground plane should be constructed so that from a desired elevation angle one could, if the ground plane were considered to be a mirror, see the image of the complete radiator 3.

A typical example of the above-described antenna, having a 75 elevation with respect to the ground plane, may incorporate the following parameters:

Screen Height 0.4 A Screen Width 0.46 A

Radiator Slant Height 0.2l A Radiator-To-Screen Distance 0.06 A

Radiator Width 0.2 A

wherein A is the longest wavelength of interest.

Because the desired radiation from the structure will be ver tically polarized, the backscreen may be constructed from a grid of parallel vertically tilted wires.

In a second embodiment, a plurality of flat radiators are mounted parallel to a reflecting screen to provide a steerable array antenna. Such an antenna array is shown in FIG. 2 wherein radiators 3, 6, and 8 are parallel to reflecting screen 2 and are supported at an angle with ground plane I by nonconducting members 10, ll, 12, 13 and 14. In said second embodiment, the same design considerations as were discussed with respect to the first embodiment are applicable. Further, the width of radiators 3, 6 and 8 may be designed to be consistent with a desired array spacing and the length of said radiators may be designed consistent with the frequency range of operation desired. These latter features are significant for the reason that the array spacing is not physically restricted by the lengths of the radiators necessary to operate over a specific frequency range.

In a third embodiment, as shown in FIG. 3, there is provided an antenna assembly comprising reflectors 2 and 18 which have one common edge; radiators 3, 6, 8, and I5, 16, 17, respectively, mounted parallel to said reflectors 2 and I8; and. a nonconducting supporting member 19 which also serves as a conduit for RF signals. Said supporting member is mechanically coupled to said reflecting surfaces and is used as a mechanical support for said antenna elements. The radiators 3, 6, 8, I5, 16 and 17 are coupled to said supporting member 19 according to techniques well known in the art.

Since the third embodiment is, in effect, a dipole version of the second embodiment, i.e., the virtual image has been replaced by a physical image and the ground plane has been removed, the design considerations which determine significant antenna parameters are the same as in the first and second embodiment.

If the overall antenna structures above described are to be broadband, a key requirement is that the antenna elements themselves be of a broadband nature. Thus, for example, folded triangular monopoles or dipoles, as well as cone monopoles or cone dipoles may be used in the place of the spade-shaped radiators previously described. For example, in a fourth embodiment, as shown in FIG. 4, there is provided a cone antenna mounted'over a ground plane 1, wherein the reflector 2 and the cone 20 are tilted with respect to said ground plane. The axis of symmetry of said cone 20a is substantially parallel with respect to said reflector 2. The supporting structure. electrical feed and design considerations are the same as described with respect to the first embodiment.

As a further example, in a fifth embodiment, as shown in FIG. 5, there is provided a folded triangular monopole antenna mounted over a ground plane wherein the reflector 2 and the folded triangular monopole 21 are tilted with respect to the ground plane 1. The axis of symmetry of said triangular monopole 21a is substantially parallel with respect to reflector 2. Again as before, the supporting structure, electrical feed and design considerations are the same as described with respect to the first embodiment.

I claim:

1. A broadband antenna comprising:

a ground plane;

antenna means having a shape substantially symmetrical along a longitudinal axis mounted at an acute angle with said ground plane; and

a backscreen reflector electrically isolated from said ground plane mounted substantially parallel to said axis of symmetry.

2. A broadband antenna, according to claim 1, wherein said antenna means includes at lease one plane-shaped conducting means.

3. A broadband antenna, according to claim 2, wherein said plane-shaped conducting means is spade-shaped.

4. A broadband antenna, according to claim 1, wherein said antenna means includes at least one cone antenna.

5. A broadband antenna, according to claim 1, wherein said antenna means includes at least one folded triangular monopole. 

1. A broadband antenna comprising: a ground plane; antenna means having a shape substantially symmetrical along a longitudinal axis mounted at an acute angle with said ground plane; and a backscreen reflector electrically isolated from said ground plane mounted substantially parallel to said axis of symmetry.
 2. A broadband antenna, according to claim 1, wherein said antenna means includes at lease one plane-shaped conducting means.
 3. A broadband antenna, according to claim 2, wherein said plane-shaped conducting means is spade-shaped.
 4. A broadband antenna, according to claim 1, wherein said antenna means includes at least one cone antenna.
 5. A broadband antenna, according to claim 1, wherein said antenna means includes at least one folded triangular monopole. 